Grain boundary studies in ordered intermetallic compound Ni3 Al

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Abstract

Theoretical and experimental studies of grain boundary structures were carried out to
understand the grain boundary properties of Ni3Al.

Using various techniques of transmission electron microscopy, the geometry of grain
boundaries was determined from a number of grain boundaries to obtain a distribution of grain
boundary types in Ni3Al. Five macroscopic parameters, including a misorientation between
two grains and a grain boundary plane orientation, were considered in the grain boundary
type. A distribution of grain boundary types in ductile Ni3Al contained more low Î£ boundaries
than brittle Ni3Al. In a distribution of grain boundary plane orientations, the trend of having
high density plane of coincident sites was maintained on low Î£ boundaries up to Î£ = 9 and
random orientations of grain boundary planes became dominant after Î£ = 11. In ductile Ni3Al,
grain boundary accommodations of dislocations in the vicinity of grain boundaries were found,
which were not shown in brittle Ni3Al. Using CBED techniques, symmetry information of a
single crystal was obtained. However, an extension to bicrystals was not successful.
In order to study the possible disordering and segregation near grain boundaries, two
different atomistic computer simulations, namely, molecular statics simulation and two dimensional
lattice gas model, were carried out. Both results showed a similar trend of disordering
near the grain boundary regardless of grain boundary composition and atomic
interaction energy assumptions. However, segregation behavior near grain boundaries showed
strong influences from grain boundary compositions and atomic interaction energy assumptions.